Fluid pressure actuated device and a gas turbine fuel control system incorporating such device

ABSTRACT

A fuel control system for a gas turbine engine has a metering valve positioned by a control fluid pressure from a device actuated by fuel pressure in response to air pressure signals obtained from the engine compressor. These pressure signals are applied to bellows units which operate through linkages to vary the effective areas of flow restrictions and thereby to provide variations in the control pressure.

United States Patent Ifield 51 3,662,546 [451 May l6, 1972 [54] FLUIDPRESSURE ACTUATED DEVICE AND A GAS TURBINE FUEL CONTROL SYSTEMINCORPORATING SUCH DEVICE [72] Inventor: Richard Joseph Ifield, NewSouth Wales,

Australia I [73] Assignee: Joseph Lucas (Industries) Limited,Birmingham, England [22] Filed: Aug. 19, 1970 [21] App]. No.: 65,008

[52] U.S. Cl ..60/39.28, 60/3916 [5 l Int. Cl. v ..F02c 9/08 [58] Fieldof Search ..60/39.28

[56] References Cited UNITED STATES PATENTS 3,394,721 7/1968 lfield..60/ 39.28 3,508,396 4/1970 Ifield ..60/39.28

Primary ExaminerClarence R. Gordon Anomey-J-lolman & Stern [57] ABSTRACTA fuel control system for a gas turbine engine has a metering valvepositioned by a control fluid pressure from a device actuated by fuelpressure in response to air pressure signals obtained from the enginecompressor. These pressure signals are applied to bellows units whichoperate through linkages to vary the effective areas of flowrestrictions and thereby to provide variations in the control pressure.

12 Claims, 2 Drawing Figures lllIlIlIllllIlI WENTEBMM 18 m2 SHEET 1 UF 2rmmmm 1', m2 1662.546

SHLEIEUFZ. I

- INVENTOR ATTORNEYS FLUID PRESSURE ACTUATED DEVICE AND A GAS TURBINEFUEL CONTROL SYSTEM INCORPORATING SUCH DEVICE This invention relates toa fluid pressure actuated device and a gas turbine fuel control systemincorporating such a device.

It has been proposed in gas turbine fuel system to actuate a fuelmetering flow regulator by an air pressure signal derived from airtappings in the compressor of the engine. The air pressure signal isderived by causing air to flow from one tapping to another through asystem of orifices, one of which is variable by a throttle control. Withthis arrangement, however, difficulties arise when the air taken fromthe compressor tappings is contaminated since blockage of the orificescan occur.

The present invention has for its object to eliminate the orifice systemand utilize only static air pressure signals. In accordance with theinvention there is provided a fluid pressure actuated device forincorporation in a gas turbine engine fuel control system, such devicecomprising a housing, a chamber within the housing first and secondpressure sensing cells in said chamber, each of which cells iscontractible by increase of a first air pressure signal applied to theinterior of the chamber, the first cell having an inlet whereby a secondair pressure signal can be applied to its interior and having one of itsends fixed within the housing, and the interior of the second cell beingevacuated, a first lever in the housing pivotable about an axis at oneot its ends, pivotal connections being formed between the other end ofthe first cell and the first lever and one end of the second cell andthe first lever, said pivotal connections being arranged at spacedpositions along the first lever, a second lever pivotally mounted at oneof its ends within the chamber and pivotally connected to the other endof the second cell, a third lever pivotally mounted in the chamber, alink interconnecting the second and third levers, an abutment associatedwith the first lever arranged to engage the third lever when the ratioof the second air pressure signal to the first air pressure signal is inexcess of a value determined by the geometry of the lever/link systemand an abutment in the chamber engageable by the first lever whensaidratio is below said value, whereby the torque applied to said thirdlever is a function of both pressure signals when said ratio exceedssaid value and a function of said first pressure signal only when saidratio is below said value.

The invention also resides in a gas turbine engine fuel control systemincorporating a device as defined above. An example of the invention isillustrated in the accompanying drawings in which:

FIG. 1 is a diagrammatic representation of part of a fuel control systemin accordance with the invention; and

FIG. 2 is a diagrammatic section through a fluid pressure actuateddevice incorporated in the system of FIG. 1.

Referring firstly to FIG. 1 the system includes a metering valve whichis rotatable in a bearing sleeve 11. The valve 10 has two triangularmetering orifices 12 which co-act with the sleeve on axial displacementof the valve 10 by a lever 13 to control the flow of fuel from a highpressure supply line 14 to two output lines 15, 16 respectivelyconnected to the main burner manifold and the pilot burner manifold ofthe associated engine 60.

The pressure drop through the valve 10 is controlled by a pressure dropunit 17 which incorporates a valve similar to the valve 10 but urgedaxially in one direction by a governor 18 and by the output fuelpressure and in the other direction by the high inlet pressure.

The lever 13 is positioned by an hydraulic piston/cylinder unit 19 whichis spring loaded to urge the valve 10 towards a minimum fuel flowposition defined by a stop 20. The pressures applied to opposite sidesof the piston of the unit 19 are controlled by an air control device 21which is shown in detail in FIG. 2.

The air control device 21 comprises a housing 22 which has three inlets23, 24 and 25. These are connected respectively to tappings in thecompressor of the engine, which is a three spool engine. Inlet 23 isconnected to the compressor intake tapping (P, inlet 24 is connected toa tapping on the delivery sideof the second compressor stage (P;,) andinlet 25 is connected to a tapping on the delivery side of the finalcompressor state (P There is also a mechanical input to the device 21such input being represented by longitudinal movement of a throttle link26.

The housing 22 contains two air chambers 27 and 28 with which the inlets24 and 23 communicate respectively. Mounted in the chamber 27 are twofluid pressure sensing cells in the form of resilient bellows 29, 30.The bellows 29 is anchored at one end of the housing and its interiorcommunicates with the inlet 25. The other end of the bellows 29 ispivotally connected to a lever 31 which is pivoted at one end to thehousing 22. As willbe evident from the drawings pressure in the chamber27 will tend to contract the bellows 29 thereby applying a force tolever 31 tending to turn it in an anticlockwise direction. Pressurewithin the bellows tends to turn the lever 31 in a clockwise direction.

The bellows 30 is evacuated and is pivotally connected at one end to asecond lever 32 which is pivoted at one end to the housing. The otherend of the bellows 30 is pivotally connected to the lever 31 at aposition on the side of the pivotal connection between lever 31 andbellows 29 remote from the pivotal mounting of the lever 31 on thehousing 22.

There is a third lever 33 pivotally mounted in the housing. This lever33 is engageable'by an abutment 34 associated with the first lever 31.In fact this abutment is, in the example described, attached to thebellows 29 but it will be appreciated that the abutment 34 could besituated at a different position on the lever 31 if required for anyspecific application. A link 35 is pivotally connected at its ends tothe levers 31 and 33 respectively.

An abutment 36 in the housing is engageable by the free end of the lever31 when the anticlockwise moments of the forces applied to this lever bythe bellows 29, 30 resulting from the air pressure signal P exceed theclockwise moment of the force applied thereto by the bellows 29 as aresult of the air pressure signal P.,. It will be appreciated fromconsideration of the geometry of the arrangement that this conditionwill occur when the ratio P,,:P is below a predetermined value.

When this ratio exceeds this value the anticlockwise moment of theforces applied to the lever 33 by the link 35 and the abutment 34 can beexpressed as follows:

where K is a constant, a is the predetermined value of said ratio and bis a constant determined by the geometry of the linkage.

When the ratio is less than a, the anticlockwise moment of the lever 33by the link 35 (the abutment 34 being out of engagement with the lever33) is given by:

A piston 37 slidable in a cylindrical bore in the housing is arranged tosupply a force for counterbalancing the anticlockwise moment on thelever 33. The piston 37 has a piston rod 38 pivoted to the lever 33 onthe side of its pivot axis remote from the link 35 and the abutment 34.The piston has an orifice 39 the effective area of which is dependent onthe proximity of the piston to the base of the bore in which the pistonslides. The piston is exposed on its side nearer the lever 33 to a lowfuel pressure and the bore is connected via a flow restrictor 40 to thehigh pressure fuel line 14. It will be appreciated that the fuelpressure in the bore will be dependent upon the spacing of the pistonfrom the base of the bore and the piston will, in fact, always take up aposition such that this fuel pressure exerts the requiredcounterbalancing pressure on the lever 33.

The chamber 28 contains a further pair of bellows 41 and 42respectively. The interior of the bellows 41 communicates with the Pinlet 25 and the bellows 42 is evacuated. The bellows 42 is pivoted to alever 43 pivoted in the housing to turn this lever in a clockwisedirection as P rises. The bellows 41 is pivoted to another lever 44which is pivoted in the housing to be turned in an anticlockwisedirection by increasing P and in a clockwise direction by increasing PThe throttle link 26 has on its end, which is inside the chamber 28, aroller unit 45 which is interposed between the levers 43 and 44. Thisarrangement is such that the lever 44 will be in equilibrium for adiflerent value of P4P, for each different position of the throttle link26.

The lever 44 has at its end remote from the bellows 41 a blade whichcontrols an orifice 46 opening into a chamber 47 connected by a passage48 to the low pressure side of piston 37. A drilling 49 extends betweenthe orifice 46 andan orifice so connected via the orifice 40 to the highpressure fuel line 14. A branch passage 51 opens into the drilling 49and this passage 51 is connected to the piston/cylinder unit 19 to urgethe piston thereof against its spring loading. A passage 52 connects thechamber 47 to the unit 19 on the opposite side of the piston thereof.

Thus, the pressure difference across the piston of unit 19 is dependentupon two separate factors, namely the relationship of P and P whichcauses variation of the fuel pressure between the orifices 40 and 50,and the relationship between P and P in relation to the setting of thethrottle link 26, which causes variation of the flow through the orifice46, an increase in pressure in passage 51 resulting in an increase infuel flow to the engine. In steady running conditions the latterrelationship is most significant in controlling the fuel flow to theengine so that there will be a specific engine running speed (at anygiven altitude) for each setting of the throttle link. During rapidacceleration the lever 44 engages a stop 53 and control of fuel flow isthen exercised in accordance with the former relationship until the P,:Pratio becomes sufiiciently high to restore the lever 44 to equilibrium.Similarly, during deceleration the lever 44 engages a stop 54.

The pressure sensitive cells 29, 30, 41 and 42 have been referred to inthe above description as bellows. It will be appreciated, however, thatdiaphragm units, or piston and cylinder units with low friction seals,could be used equally.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

l. A fluid pressure actuated device for incorporation in a gas turbineengine fuel control system, the said device comprising a housing, achamber within the housing, first and second pressure sensing cells insaid chamber, each of which cells is contractible by increase of a firstair pressure signal applied to the interior of the chamber, the firstcell having an inlet whereby a second air pressure signal can be appliedto its interior and having one-of its ends fixed within the housing, andthe interior of the second cell being evacuated, a first lever in thehousing pivotable about an axis at one of its ends,

pivotal connections being formed between the other end of the first celland the first lever and one end of the second cell and the first lever,said pivotal connections being arranged at spaced positions along thefirst lever, a second lever pivotally mounted at one of its ends withinthe chamber and pivotally connected to the other end of the second cell,a third lever pivotally mounted in the chamber, a link interconnectingthe second and third levers, an abutment associated with the first leverarranged to engage the third lever when the ratio of the second airpressure signal to the first air pressure signal is in excess of a valuedetermined by the geometry of the lever/link system and an abutment inthe chamber engageable by the first lever when said ratio is below saidvalue, whereby the torque applied to said third lever is a function ofboth pressure signals when said ratio exceeds said value and a functionof said first pressure signal only when said ratio is below said value.

2. A device as claimed in claim 1 which includes first and second liquidflow restricting orifices connected in series, the effective area of thefirst orifice being variable in accordance with the torque applied tothe said third lever, a restricted inlet for a fluid under pressurebetween the first and second orifices, an outlet for a fluid pressuresignal on a side of the second orifice remote from t e first or ice anda port for connection to a low pressure on a side of the first orificeremote from the inlet.

3. A device as claimied in claim 2 which includes a piston displaceablein one direction by the fluid pressure between said first and secondorifices and in the opposite direction by movement of the third lever inresponse to increases in the second air pressure signal.

4. A device as claimed in claim 3 in which movement of the piston in thesaid one direction increases the effective area of the first orifice.

5. A device as claimed in claim 4 which includes a further chamberwithin the housing, third and fourth pressure sensing cells in the saidfurther chamber, contractible by increase of a third air pressure signalapplied to the interior of the further chamber, the third cell having aninlet whereby the said second air pressure signal can be applied to itsinterior, one end of both the third and fourth cells being fixed withinthe housing, and the interior of the fourth cell being evacuated, afourth lever pivotal within the housing and pivotally connected to theother end of the third cell, a fifth lever pivoted about one of its endswithin the housing and pivotally connected to the other end of thefourth cell and a member movable within the housing and providing apivotal engagement between the fourth and fifth levers, the location ofthe said pivotal engagement being variable by movement of the member.

6. A device as claimed in claim 5 which includes a third fluid flowrestricting orifice, one side of which communicates with the said fluidpressure signal outlet and whose effective area is variable by thefourth lever and a port on a side of the third orifice remote the saidinlet for connection to a low pressure.

7. A device as claimed in claim 6 in which the port associated with thethird flow restricting orifice communicates with the port associatedwith the first flow restricting orifice.

8. A device as claimed in claim 5 which includes means for limiting thetravel of the fourth lever.

9. A fuel control system for a gas turbine engine including acompressor, the said control system comprising a fluid pressure actuateddevice as claimed in claim 2, a metering valve for the fuel andactuating means for the metering valve, said actuating means beingresponsive to a fluid pressure signal at said outlet of the device.

10. A fuel control system for a gas turbine engine including acompressor, said control system comprising a fluid pressure actuateddevice as claimed in claim 5, a metering valve for the fuel andactuating means for the metering valve, said actuating means beingresponsive to a fluid pressure signal at said outlet of the device, saidsystem including a throttle control and the member pivotally engagingthe fourth and fifth levers being operatively connected to said throttlecontrol.

11. A fuel control system as claimed in claim 10 in which the airpressure signals applied to the pressure sensing cells are derived fromthe engine compressor.

12. A fuel control system as claimed in claim 11 in which the liquidapplied to the inlet of the said device is a fuel for the engine.

1. A fluid pressure actuated device for incorporation in a gas turbineengine fuel control system, the said device comprising a housing, achamber within the housing, first and second pressure sensing cells insaid chamber, each of which ceLls is contractible by increase of a firstair pressure signal applied to the interior of the chamber, the firstcell having an inlet whereby a second air pressure signal can be appliedto its interior and having one of its ends fixed within the housing, andthe interior of the second cell being evacuated, a first lever in thehousing pivotable about an axis at one of its ends, pivotal connectionsbeing formed between the other end of the first cell and the first leverand one end of the second cell and the first lever, said pivotalconnections being arranged at spaced positions along the first lever, asecond lever pivotally mounted at one of its ends within the chamber andpivotally connected to the other end of the second cell, a third leverpivotally mounted in the chamber, a link interconnecting the second andthird levers, an abutment associated with the first lever arranged toengage the third lever when the ratio of the second air pressure signalto the first air pressure signal is in excess of a value determined bythe geometry of the lever/link system and an abutment in the chamberengageable by the first lever when said ratio is below said value,whereby the torque applied to said third lever is a function of bothpressure signals when said ratio exceeds said value and a function ofsaid first pressure signal only when said ratio is below said value. 2.A device as claimed in claim 1 which includes first and second liquidflow restricting orifices connected in series, the effective area of thefirst orifice being variable in accordance with the torque applied tothe said third lever, a restricted inlet for a fluid under pressurebetween the first and second orifices, an outlet for a fluid pressuresignal on a side of the second orifice remote from the first orifice anda port for connection to a low pressure on a side of the first orificeremote from the inlet.
 3. A device as claimied in claim 2 which includesa piston displaceable in one direction by the fluid pressure betweensaid first and second orifices and in the opposite direction by movementof the third lever in response to increases in the second air pressuresignal.
 4. A device as claimed in claim 3 in which movement of thepiston in the said one direction increases the effective area of thefirst orifice.
 5. A device as claimed in claim 4 which includes afurther chamber within the housing, third and fourth pressure sensingcells in the said further chamber, contractible by increase of a thirdair pressure signal applied to the interior of the further chamber, thethird cell having an inlet whereby the said second air pressure signalcan be applied to its interior, one end of both the third and fourthcells being fixed within the housing, and the interior of the fourthcell being evacuated, a fourth lever pivotal within the housing andpivotally connected to the other end of the third cell, a fifth leverpivoted about one of its ends within the housing and pivotally connectedto the other end of the fourth cell and a member movable within thehousing and providing a pivotal engagement between the fourth and fifthlevers, the location of the said pivotal engagement being variable bymovement of the member.
 6. A device as claimed in claim 5 which includesa third fluid flow restricting orifice, one side of which communicateswith the said fluid pressure signal outlet and whose effective area isvariable by the fourth lever and a port on a side of the third orificeremote the said inlet for connection to a low pressure.
 7. A device asclaimed in claim 6 in which the port associated with the third flowrestricting orifice communicates with the port associated with the firstflow restricting orifice.
 8. A device as claimed in claim 5 whichincludes means for limiting the travel of the fourth lever.
 9. A fuelcontrol system for a gas turbine engine including a compressor, the saidcontrol system comprising a fluid pressure actuated device as claimed inclaim 2, a metering valve for thE fuel and actuating means for themetering valve, said actuating means being responsive to a fluidpressure signal at said outlet of the device.
 10. A fuel control systemfor a gas turbine engine including a compressor, said control systemcomprising a fluid pressure actuated device as claimed in claim 5, ametering valve for the fuel and actuating means for the metering valve,said actuating means being responsive to a fluid pressure signal at saidoutlet of the device, said system including a throttle control and themember pivotally engaging the fourth and fifth levers being operativelyconnected to said throttle control.
 11. A fuel control system as claimedin claim 10 in which the air pressure signals applied to the pressuresensing cells are derived from the engine compressor.
 12. A fuel controlsystem as claimed in claim 11 in which the liquid applied to the inletof the said device is a fuel for the engine.